managing resources

• Controlling development


  1. Organism begins as single cell

  2. Cells divide

  3. Cells differentiate and specialise
• Gene expression


  Switching on or switching off the expression of a gene determines the development of features within an organism
• Gene expression regulation


  Transcription factors bind to specific DNA sequences to control the rate of transcription of genes
• Homeobox gene


  Contains a short (180 bases) region called the homeobox which codes for a part of the protein (60 amino acids) called the homeobox domain or homeodomain
• The homeobox sequence is highly conserved and found in plants, animals and fungi
• Homeodomain proteins


  • Regulate transcription of other genes
  • Have a characteristic shape that binds to the enhancer region of genes, initiating or enhancing transcription
• The shape of the homeodomain is alpha helices 2 and 3 forming a specific structure known as H-T-H (helix turn helix)
• Hox genes


  A subset of homeobox genes only found in animals that control the head-to-tail development of embryos
• Hox genes ensure that body parts grow in the correct places
• Hox gene clusters


  Groups of Hox genes that control the development of the embryo in sequence: head, thorax, abdomen
• In the mouse, 13 Hox genes in 4 clusters control the development of the head, thorax and abdomen
• The same Hox genes are duplicated and found in humans
• Hox genes control the body plan of an embryo along the axis (head–to-tail)
• Mutations in Hox gene binding regions

  Transcription factors unable to regulate transcription of genes, organisms not viable or have reduced survival
• Organisms with Hox gene mutations


  Unlikely to survive to reproduce, selected against
• Mutations in transcription factor binding sites face negative selection pressure
• The linear order of the Hox genes within the clusters relates to the sequential order of the regions in the body
• Body symmetry


  • Beetle has bilateral symmetry
  • Coral has radial symmetry
  • Sponge has no symmetry - Asymmetry
• Fruit flies were studied due to their low sentience, lack of pain sensation, small size, short life cycle, low cost, and fewer chromosomes